Baseline demographics and clinical characteristics of the overall population with JIA, the population with JIA with at least one additional autoimmune disease or associated condition (JIA+) and the population with JIA without an additional autoimmune disease or associated condition (JIA–)
| Characteristic | Overall population with JIA (n=1332) | JIA+ (n=247) | JIA– (n=1085) | P value |
| Sex, female, n (%) | 867 (65.1) | 168 (68.0) | 699 (64.4) | 0.29 |
| Age at JIA onset, years, mean (SD) | 6.6 (4.5) | 7.4 (4.5) | 6.4 (4.5) | 0.02 |
| Age at diagnosis, years, mean (SD) | 8.0 (4.8) | 9.0 (4.9) | 7.8 (4.7) | 0.001 |
| JIA subtype, n (%) | <0.001 | |||
| Oligoarticular | 360 (27.0) | 59 (23.9) | 301 (27.7) | |
| Polyarticular RF-negative | 320 (24.0) | 50 (20.2) | 270 (24.9) | |
| Missing* | 303 (22.7) | 45 (18.2) | 258 (23.8) | |
| Systemic | 90 (6.8) | 37 (15.0) | 53 (4.9) | |
| Enthesitis-related | 88 (6.6) | 25 (10.1) | 63 (5.8) | |
| Psoriatic | 72 (5.4) | 10 (4.0) | 62 (5.7) | |
| Undifferentiated | 65 (4.9) | 15 (6.1) | 50 (4.6) | |
| Polyarticular RF-positive | 30 (2.3) | 4 (1.6) | 26 (2.4) | |
| Unclassified† | 4 (0.3) | 2 (0.8) | 2 (0.2) | |
| Autoimmune diseases ever, n (%) | <0.001 | |||
| 0 | 1085 (81.5) | 0 (0) | 1085 (100.0) | |
| 1 | 214 (16.1) | 214 (86.6) | 0 (0) | |
| 2 | 30 (2.3) | 30 (12.1) | 0 (0) | |
| 3 | 2 (0.2) | 2 (0.8) | 0 (0) | |
| >3 | 1 (0.1) | 1 (0.4) | 0 (0) | |
| Medication ever, n (%) | ||||
| Biological DMARDs | 800 (60.1) | 181 (73.3) | 619 (57.1) | <0.001 |
| Non-biological DMARDs | 862 (64.7) | 177 (71.7) | 685 (63.1) | 0.01 |
| Methotrexate | 797 (59.8) | 158 (64.0) | 639 (58.9) | 0.14 |
| Corticosteroids | 768 (57.7) | 175 (70.9) | 593 (54.7) | <0.001 |
| NSAIDs | 1201 (90.2) | 234 (94.7) | 967 (89.1) | 0.01 |
*The JIA subtype was not indicated in the electronic health records.
†Patient received only one ICD code for JIA.
DMARDs, disease-modifying antirheumatic drugs; ICD, International Classification of Diseases; JIA, juvenile idiopathic arthritis; NSAIDs, non-steroidal anti-inflammatory drugs; RF, rheumatoid factor; SD, standard deviation.